\begin{tikzpicture}[
node distance = 2cm and 2cm,
     N/.style = {circle, draw, font=\Large, 
                 minimum size=1.1em},
       every edge/.style = {draw, -Stealth, semithick, shorten >=2pt},
every edge quotes/.style = {auto=right, inner sep=2pt}
                        ]
\node[N] (a)[label=left :{+}] {1};
\node[N] (b)[right of=a]{2};
\node[N] (c)[right of=b][label=right :{-}]{3};
\node (a1) at ([xshift=-1em,yshift=2em]a.north){FA2:};
\path
(a) edge [above] node {a} (b)
(b) edge [above] node {b} (c)
(c) edge [bend left,below] node {a} (b)
% (b) edge [loop above] node {b} (b)
    % edge [loop above] node {b} ()
% (d) edge [loop above] node {b} ()
    ;
    \end{tikzpicture}